This invention relates to an interface circuit for transferring data from a central processing unit (hereinafter called "CPU") to a peripheral device like a liquid crystal display (hereinafter called "LCD") at high speed. This invention also relates particularly to an interface circuit which has taken countermeasures against noise produced incident to the transfer of data at high speed.
An interface circuit has a shift register supplied with a clock signal indicative of data transfer timing and a start signal indicative of the start of data transfer from a CPU, and a data latch which is sequentially supplied with display data from the CPU and holds these data therein for their display.
A display unit such as an LCD or the like has recently been increased in screen size. With its increase, the amount of data to be transmitted is increasing. A display cycle per screen is substantially determined depending on human eye's characteristics. Thus, the increase in the amount of data must be solved by the speeding up of a transfer rate. The speeding up of the transfer rate needs to increase the frequency of a data transfer clock signal. However, the increase in the frequency of the clock signal will increase a current to be used up or consumed by an interface circuit.
When the frequency of the clock signal is made greater, a high-frequency signal is radiated outside, so-called EMI (Electromagnetic Interference) noise is produced.